The Section provides expert physical and technological support for radiation treatment. This support consists of routine calibration and quality assurance of all radiation equipment and includes special dosimetry studies, computer-assisted treatment planning, and the design and development of special equipment tailored to special clinical needs. Regular checking of dosimetric and technical set-up aspects of radiation treatment to be continued. 1. An efficiently graded quality assurance program, originally developed for the two Siemens linear accelerators, has been adapted and extended for the three Varian accelerators (Clinacs 4, 18, and 20). 2. Adaptation of the new radiation equipment has been performed and special supporting equipment for patient treatment has been developed and implemented. 3. The Clinac 4/100 and Clinac 18 linear accelerators are now fully operational. The Clinac 20 has been accepted, but a great amount of special work is needed to be done in preparation for the temporary transfer of the intra-operative irradiation program to this machine. Also, preparatory work for total skin and total body irradiation is in progress. 4. A special adaptation of an existing operating table has been designed for use in the intra-operative program. Construction is well underway. 5. The computer programs for clinical radiation treatment planning have been further extended in all three subfields: external beam, point-source, and line-source radiation fields.